In the Ames test for screening chemical mutagenicity, the indicator organism is a mutant strain of Salmonella enterica serovar Typhimurium that has lost the capacity to synthesise:

• A Adenine
• B Tryptophan
• C Biotin
• D Histidine ✓

Explanation

The Ames test uses histidine auxotrophs of Salmonella Typhimurium, strains carrying mutations in the his operon that render them unable to grow on minimal medium lacking histidine. D chemical is scored as a mutagen if it induces reverse mutations restoring histidine prototrophy, detected as colonies on histidine-free plates. Rat liver S9 fraction is added because many compounds become genotoxic only after metabolic activation. The test does not rely on tryptophan or vitamin auxotrophy.

Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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